In key California House races, Republicans are turning...

1of3VoteCrew creator and Rise California member Maxwell Lubin (right) talks with Associated Students of the University of California external vice president Nuha Khalfay during a Sept. 25 event at UC Berkeley encouraging students to vote.Photo: Michael Short / Special to The Chronicle

2of3Elections department employees count the early vote-by-mail ballots at SF City Hall on Tuesday, Oct. 30, 2018, in San Francisco, Calif.Photo: Liz Hafalia / The Chronicle

With the midterm elections just days away, there’s little indication that California is seeing a “blue wave” of Democratic votes, at least in the early returns of vote-by-mail ballots — and in some key races that will help determine control of the House, Republican voter response has been strong.

There are still a lot more ballots to come in, cautioned Paul Mitchell, vice president of Political Data Inc., which supplies voter information to a variety of political campaigns. But so far, according to a mail ballot tracker he runs, Republican votes are keeping pace with the number of Democratic ballots.

“Looking at the comparable numbers, the statewide mail ballot returns at this point are running about 40 percent higher than the primary, 1.7 million to 1.2 million,” he said.

For example, in Orange County’s 45th Congressional District, where Republican Rep. Mimi Walters is running against Democrat Katie Porter, the vote-by-mail return by the weekend was almost double what it was at the same point in the June primary, Mitchell said. In the 48th district, where GOP Rep. Dana Rohrabacher of Costa Mesa (Orange County) is being challenged by Democrat Harley Rouda, the number of mail-in ballots was up 84 percent.

But the boost might not be helping Democrats. In the Walters versus Porter race, for example, Democrats made up 31 percent of those who received mail ballots, while Republicans made up 37 percent. As of Monday, however, the total number of ballots coming back favored Republicans, 45 percent to 31 percent. The numbers were similarly lopsided in Rohrabacher’s district, while in the Denham versus Harder race, Democratic and Republican returns were about even.

That’s not really a surprise, Mitchell said, since the first ballot returns typically skew toward Republicans.

“Traditionally, these early returns represent voters who are homeowners, more affluent and more white,” he said. “These are people who vote in every election.”

While Democrats like billionaire investor Tom Steyer have put millions of dollars into efforts to bring young people out to vote in this year’s midterm elections, there’s little sign that’s working in California, at least so far.

“One of the most striking statistics is that voters 18 to 34 and those 65 and older each make up about a quarter of California’s registered voters,” Mitchell said. But in the early mail voting returns, he said, “seniors make up about half of those ballots, while younger voters are less than 1 in 10.”

In the Orange County district represented by retiring GOP Rep. Ed Royce of Fullerton, Republican Young Kim is locked in a tight battle with Democrat Gil Cisneros. But only 9 percent of the returned ballots there come from voters ages 18-34, who tend to vote Democratic. That’s compared to the 48 percent from seniors, who are more likely to back Republicans.

“Maybe some of it is young voters who don’t know where they keep the stamps, but if you believe the hype about the blue wave, we should start to see some changes” as election day approaches, Mitchell said.

The late ballots and those turned in on election day tend to be from Democratic voters, but there has to be a significant uptick to flip California districts that Republicans, in many cases, have held for decades.

And a surge in Democratic turnout, both in mail ballots and at the polls, may not be enough to oust GOP officeholders if Republicans can match that enthusiasm.

“You have to see Democrats do better in those targeted seats to win,” Mitchell said. “If both parties are doing better, that might not be good enough for Democrats.”

John Wildermuth is a native San Franciscan who has worked as a reporter and editor in California for more than 40 years and has been with the San Francisco Chronicle since 1986. For most of his career, he has covered government and politics. He is a former assistant city editor and Peninsula bureau chief with The Chronicle and currently covers politics and San Francisco city government.